In modern engine technology, turbochargers are powered by the hot exhaust gas from the engine. In general, the higher the exhaust velocity, the greater the amount of power in the exhaust that is available to power the turbochargers. It is desirable to convey the hot exhaust gas from the engine to the turbocharger in as high a temperature state as is possible to maintain the exhaust gas volume and, therefore, velocity in the exhaust system. However, it is also desirable to reduce the temperature of components within the engine compartment. Prior techniques provide water jackets disposed about exhaust manifolds to reduce the temperature of the manifold. Unfortunately, the use of water jackets reduces the temperature of the exhaust gas, thereby reducing the energy supplied to the turbocharger and also the temperature of recoverable heat energy.
Some attempts have been made to produce a manifold with temperatures within allowable limits and, at the same time, to maintain the temperature of the exhaust gas as high as possible. One such system described in U.S. Pat. No. 5,463,867 (“the '867 patent”) provides a sleeve inside the manifold which is surrounded by an air space. The air space provides insulation for maintaining the exhaust gas temperature as high as possible and, at the same time, to reduce the amount of heat transferred to the water of the water jacket. However, the flow of the exhaust gasses within this system is restricted by the geometry of the connection pipes between the cylinder outlets and the exhaust pipe. As such, in the '867 patent and other systems, exhaust gas velocity is reduced.
Some other, non-water jacketed, exhaust systems such as U.S. Pat. No. 6,745,561 attempt to retain exhaust gas velocity by converging a set of runners in a manifold. However, turbulent exhaust flow is still present at the convergence of the runners and the overall shape of the resulting manifold is not conducive to jacketing.
Accordingly, there is a need for an improved exhaust system to address the problems described above and/or problems posed by other conventional approaches.